Vassalli J D, Baccino D, Belin D
J Cell Biol. 1985 Jan;100(1):86-92. doi: 10.1083/jcb.100.1.86.
The secretion of plasminogen activators has been implicated in the controlled extracellular proteolysis that accompanies cell migration and tissue remodeling. We found that the human plasminogen activator urokinase (Uk) (Mr 55,000 form) binds rapidly, specifically, and with high affinity to fresh human blood monocytes and to cells of the monocyte line U937. Upon binding Mr 55,000 Uk was observed to confer high plasminogen activator activity to the cells. Binding of the enzyme did not require a functional catalytic site (located on the B chain of the protein) but did require the noncatalytic A chain of Mr 55,000 Uk, since Mr 33,000 Uk did not bind. These results demonstrate the presence of a membrane receptor for Uk on monocytes and show a hitherto unknown function for the A chain of Uk: binding of secreted enzyme to its receptor results in Uk acting as a membrane protease. This localizes plasminogen activation near the cell surface, an optimal site to facilitate cell migration.
纤溶酶原激活剂的分泌与伴随细胞迁移和组织重塑的可控细胞外蛋白水解有关。我们发现人纤溶酶原激活剂尿激酶（Uk）（55,000分子量形式）能快速、特异性且高亲和力地结合新鲜人血单核细胞及单核细胞系U937的细胞。结合后，观察到55,000分子量的Uk赋予细胞高纤溶酶原激活剂活性。该酶的结合不需要功能性催化位点（位于蛋白的B链上），但确实需要55,000分子量Uk的非催化A链，因为33,000分子量的Uk不结合。这些结果证明单核细胞上存在Uk的膜受体，并揭示了Uk的A链迄今未知的功能：分泌的酶与其受体结合导致Uk作为膜蛋白酶起作用。这将纤溶酶原激活定位在细胞表面附近，这是促进细胞迁移的最佳位点。
